## Wednesday, 30 May 2012

After the exam madness, I'm about to leave sunny England and off to relatively frosty Trondheim to attend and give a talk at the Second Workshop on Bayesian Inference for Latent Gaussian Models with Applications. Looks like a very interesting small conference, with lots of good talks.

Of course, I haven't finished preparing mine (but I'm unusually nearly there). I'll talk about my work on hierarchical models for data on In Vitro Fertilisation (IVF) and pre-implantation genetic screening (PGS). The main issue is that while we (or rather "they") are very good at fertilising eggs in a dish, we (again: they) are not so good at actually making the resulting embryo implant in the mother's womb, which means that the actual pregnancy rate is overall still about 30$-$40%.

The main problem is that once the eggs have been collected and fertilised, they are followed up for a few days after which the embryologist looks at them and decides which ones "look good"; these are then put back in the womb and hopefully develop in a pregnancy. But this of course does not account for potential problems in the genetic structure of the embryos, which are invisible to the naked eye. PGS is a complex genetic test that is able to detect potential chromosomal abnormalities in the embryos, thus making the choice of which are the "best" more informed.

The theory that we are testing is that shorter telomere (some kind of protective cap sitting at the end of the chromosomes) are associated with chromosomal abnormalities. The nature of the data is obviously hierarchical, because normally we observe different cells, each of which belongs to one embryo, each of which is donated for research by a couple of parents. However, in this field there aren't many papers using appropriate methods to account for the implied correlation among the observations (in fact, I think there aren't any at all).

Our work seems to suggest that there is indeed some association between the length of telomere and chromosomal abnormalities $-$ especially for embryos that are not well developed.

For "minor chaotic" embyros, which are as good as it gets in this setting, there doesn't seem to be any (or at least hardly any) effect of the length of telomere. In a way, even for the more problematic embryos (up to "uniformally abnormal", which are really screwed up) the effect is not very large and the probability of testing positive at PGS is not very much affected by the length of telomere. But for the intermediate embryos, the chance of testing positive to PGS is actually very much affected by telomere's length.

There are then potentially very important implications for the underlying science and for the management of IVF patients.

I'll post some more when I have finished the presentation. Also, we are working on a paper (just need to finalise a couple of details and re-submit it after having pleased the referees' thirst for modifications...)

1. Interesting conference, although slightly unbalanced towards spatial models $-$ nearly all talks (but mine and a couple more) were heavily discussing these kind of models.